Variable voltage compliance for current output generator

ABSTRACT

A system for providing stimulation current in implantable medical devices is provided. One aspect of this disclosure relates to an apparatus including a power supply terminal adapted to be connected to a power supply. The apparatus embodiment also includes circuitry connected to the power supply terminal and adapted to detect a parameter dependent on tissue/electrode impedance. The apparatus embodiment further includes a current output pulse generator adapted to deliver electrical therapy. The current generator includes an adjustable compliance voltage source connected to the power supply terminal. The compliance voltage source has a programmable amplitude and is adapted to provide different potentials for different tissue/electrode interface impedances. According to various embodiments, the apparatus embodiment also includes at least one stimulating electrode, and the current generator is adapted to deliver electrical therapy using the electrode. Other aspects and embodiments are provided herein.

CLAIM OF PRIORITY

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 11/457,385,filed on Jul. 13, 2006, which is hereby incorporated by reference hereinin its entirety.

TECHNICAL FIELD

This disclosure relates generally to implantable medical devices and,more particularly, to systems for providing stimulation current.

BACKGROUND

Current output devices, as compared to voltage output devices, mayprovide superior neural recruitment characteristics during neuralstimulation from an implantable medical device (IMD). However, thecurrent output device requires a compliance voltage sufficient to drivestimulation current through a tissue/electrode interface. Because ofvariation in tissue/electrode interface impedance, the compliancevoltage requirements can negatively impact battery longevity. Thus,there is a need for improved systems for providing stimulation currentin implantable medical devices.

SUMMARY

Disclosed herein, among other things, is system for providingstimulation current from an implantable medical device. One aspect ofthis disclosure relates to an apparatus including a power supplyterminal adapted to be connected to a power supply. The apparatusembodiment also includes circuitry connected to the power supplyterminal and adapted to detect a parameter dependent on tissue/electrodeimpedance. The apparatus embodiment further includes a current outputpulse generator adapted to deliver electrical therapy. The currentgenerator includes an adjustable compliance voltage source connected tothe power supply terminal. The compliance voltage source has aprogrammable amplitude and is adapted to provide different potentialsfor different tissue/electrode interface impedances.

An apparatus embodiment includes a power supply and circuitry adapted todetect tissue/electrode impedance and further adapted to be connected tothe power supply. The apparatus embodiment also includes a currentoutput pulse generator adapted to deliver electrical therapy. Thecurrent generator includes an adjustable compliance voltage sourceconnected to the power supply. The compliance voltage source has aprogrammable amplitude and is adapted to provide different potentialsfor different tissue/electrode interface impedances. According tovarious embodiments, the apparatus embodiment also includes at least onestimulating electrode, and the current output pulse generator is adaptedto deliver electrical therapy using the electrode.

One aspect of this disclosure relates to a method for making a systemfor providing stimulation current from an implantable medical device. Anembodiment of the method includes forming circuitry adapted to detect aparameter dependent on tissue/electrode impedance. The method embodimentalso includes forming a current output pulse generator adapted todeliver electrical therapy, the generator including a compliance voltagesource having a programmable amplitude and adapted to provide differentpotentials for different tissue/electrode interface impedances.

One aspect of this disclosure relates to a method for providingstimulation current from an implantable medical device. An embodiment ofthe method includes applying electrical stimulation therapy using acurrent output pulse generator having an adjustable compliance voltagesource. The method embodiment also includes detecting a parameterdependent on tissue/electrode interface impedance. The method embodimentfurther includes adjusting the level of the voltage source based on thedetected parameter.

This Summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a system for providing stimulationcurrent, according to one embodiment.

FIG. 2 illustrates a schematic diagram of a current source for providingstimulation current, according to one embodiment.

FIG. 3A illustrates a cuff electrode for use with a system for providingstimulation current, according to one embodiment.

FIG. 3B illustrates a transvascular electrode for use with a system forproviding stimulation current, according to one embodiment.

FIG. 4 illustrates a block diagram of a system with an IMD for providingstimulation current, according to one embodiment.

FIG. 5 illustrates a block diagram of a programmer such as illustratedin the system of FIG. 4 or other external device to communicate with theIMD(s), according to one embodiment.

FIG. 6 is illustrates block diagram illustrating an embodiment of anexternal system to communicate with the IMD(s), according to oneembodiment.

FIG. 7 illustrates a flow diagram of a method for making a system forproviding stimulation current from an IMD, according to one embodiment.

FIG. 8 illustrates a flow diagram of a method for providing stimulationcurrent from an implantable medical device, according to one embodiment.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingswhich show, by way of illustration, specific aspects and embodiments inwhich the present invention may be practiced. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention. Other embodiments may be utilized andstructural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

The present disclosure provides a system for providing stimulationcurrent using a current output device, or current pulse generator.Current output devices, as compared to voltage output devices, mayprovide superior neural recruitment characteristics during neuralstimulation. However, the current output device requires a compliancevoltage sufficient to drive stimulation current through atissue/electrode interface impedance. The present disclosure providesfor a variable compliance voltage that can be adjusted based on pulseamplitude and/or a detected impedance value, conserving power andthereby improving battery longevity.

System for Providing Stimulation Current

FIG. 1 illustrates a block diagram of a system for providing stimulationcurrent, according to one embodiment. The depicted apparatus 100includes a power supply terminal 102 adapted to be connected to a powersupply 104. The apparatus embodiment also includes circuitry 106connected to the power supply terminal and adapted to detect a parameterdependent on impedance at an interface of at least one electrode 112 andtissue to be stimulated by the electrode (tissue/electrode interfaceimpedance or tissue/electrode impedance). The apparatus embodimentfurther includes a current output pulse generator 108 adapted to deliverelectrical therapy, the generator including an adjustable compliancevoltage source 110 connected to the power supply terminal, thecompliance voltage source having a programmable amplitude and adapted toprovide different potentials for different tissue/electrode interfaceimpedances.

According to various embodiments, the voltage source 110 is adjustedusing an electronic feedback loop to maintain a fixed voltagedifferential between the compliance voltage and a load voltage. Thevoltage source 110 is adjusted using a look-up table that includes adetected tissue/electrode interface impedance and a desired level ofstimulation current, according to various embodiments. The voltagesource can be adjusted using an external device. The external device canadjust the voltage source using a detected tissue/electrode interfaceimpedance and a desired level of stimulation current. Examples ofexternal devices, such as depicted in FIGS. 5 and 6, include advancedpatient management systems (APM), programmers, handheld devices, andother remote devices capable of communication with an implantedapparatus.

An apparatus embodiment includes a power supply and circuitry adapted todetect tissue/electrode impedance and further adapted to be connected tothe power supply. The apparatus embodiment also includes a currentoutput pulse generator adapted to deliver electrical therapy, thegenerator including an adjustable compliance voltage source connected tothe power supply, the compliance voltage source having a programmableamplitude and adapted to provide different potentials for differenttissue/electrode interface impedances. According to various embodiments,the apparatus embodiment also includes at least one stimulatingelectrode, and the current output pulse generator is adapted to deliverelectrical therapy using the electrode. The voltage source can beadjustable over a range from 1V to 100V and values of tissue/electrodeinterface impedance include a range of impedance values from 100Ω to 10kΩ, according to various embodiments. According to various embodiments,the current output pulse generator can be adapted to deliver electricalcurrent over a range from 5 μA to 10 mA.

The apparatus can further include at least one stimulating electrode112, wherein the current output pulse generator is adapted to deliverelectrical therapy using the at least one electrode. Types of electrodesused to deliver therapy include transvacular and nerve cuff electrodes,as shown in FIGS. 3A and 3B. Other electrodes may be used withoutdeparting from the scope of this disclosure. Types of electrical therapythat can be delivered include cardiac rhythm management therapy andneural stimulation therapy such as vagal stimulation therapy. Othertypes of electrical therapy can be delivered by the disclosed apparatuswithout departing from the scope of this disclosure.

A system embodiment includes means for applying neural stimulation usinga current output pulse generator having an adjustable compliance voltagesource. The system embodiment also includes means for detecting atissue/electrode interface impedance or a parameter dependent on thetissue/electrode interface impedance. The system embodiment furtherincludes means for adjusting the level of the voltage source connectedto the detecting means and the stimulating means. According to variousembodiments, the applying means includes an implantable medical device.The detecting means includes a sensor and circuitry to monitor thesensor, according to various embodiments. The detecting means caninclude at least one electrode.

According to an embodiment, the means for adjusting the voltage sourceincludes means for adjusting the voltage source based on a programmedamplitude of the current pulse generator. The means for adjusting thevoltage source includes means for adjusting the voltage source based ondetected tissue/electrode interface impedance, according to anembodiment. The means for adjusting the voltage source includes meansfor adjusting the voltage source based on programmed amplitude of thecurrent source and detected tissue/electrode interface impedance, in anembodiment. According to various embodiments, the system is fullyimplantable. Only the stimulating means and detecting means areimplantable, in an embodiment. The system further includes an enclosure,in an embodiment. The enclosure is adapted to house the stimulatingmeans, detecting means and adjusting means in one embodiment, and isadapted to house only the stimulating means and detecting means, inanother embodiment.

FIG. 2 illustrates a schematic diagram of a current source for providingstimulation current, according to one embodiment. The current source 200includes a compliance voltage that includes the voltage level on supplycapacitor 210. The current source 200 is used to deliver electricaltherapy to electrodes 220 as shown with variable current sources I1 andI2. A number of switches 230 are used to control the delivery ofelectrical stimulation therapy. The switches 230 may be embodied astransistors or other switching electrical devices. The P and Rdesignations indicate which phase is being delivered. P denotes pacingor the stimulation portion of the waveform 240 and R denotes recharge orthe charge equalization portion of the waveform. The supply capacitor210 is charged to a voltage level, the voltage level determined bymultiplying the desired current by the detected impedance at theelectrode/tissue interface, according to various embodiments. Theimpedance at the interface of the electrode and tissue can be detectedor measured using a number of techniques. According to an embodiment,the electrode/tissue interface impedance is detected by forcing a knowncurrent to the electrodes and measuring the voltage at the stimulationterminals (electrodes). The electrode/tissue interface impedance isdetected by applying a constant voltage to the electrodes and measuringthe current through the electrodes, according to one embodiment. In anembodiment, the electrode/tissue interface impedance is detected byconnecting a charged capacitor the stimulation electrodes for apre-determined amount of time, and measuring the voltage differenceacross the capacitor before and after connecting it to the electrodes.The electrode/tissue interface impedance can also be detected byconnecting a charged capacitor to the stimulation electrodes until thevoltage difference across this capacitor achieves a predetermined value,and measuring the amount of time it takes to achieve the value,according to an embodiment.

Neural Stimulation

Neural stimulation has been the subject of a number of studies and hasbeen proposed for several therapies. The autonomic system controlsphysiological activities of the body and the imbalance of autonomic toneis related to many diseases and conditions. Reduced autonomic balance(increase in sympathetic and decrease in parasympathetic cardiac tone)during heart failure has been shown to be associated with leftventricular dysfunction and increased mortality. Sympathetic inhibition,as well as parasympathetic activation, has been associated with reducedarrhythmia vulnerability following a myocardial infarction. Vagus nervestimulation has been proposed to treat sleep disorders, gastrointestinalmotility, eating disorders, obesity, anorexia, gastrointestinal tractdisorders, hypertension, coma, and epilepsy. Direct electricalstimulation of parasympathetic nerves can activate the baroreflex,inducing a reduction of sympathetic nerve activity and reducing bloodpressure by decreasing vascular resistance. Direct stimulation of thevagal parasympathetic fibers has been shown to reduce heart rate via thesympathetic nervous system. In addition, some research indicates thatchronic stimulation of the vagus nerve may be of protective myocardialbenefit following cardiac ischemic insult.

The neural stimulation can be applied to a vagus nerve, a cardiac branchof the vagus nerve, a cardiac fat pad, a baroreceptor site, or to otherneural targets that stimulate the parasympathetic nervous system orinhibit the sympathetic nervous system. The neural stimulation can beapplied using intravascularly-fed electrodes, nerve cuffs, satelliteelectrodes, and other known means for stimulating a neural target. FIG.3A illustrates a cuff electrode for use with a system for providingstimulation current, according to one embodiment. The cuff electrode 302is placed around nerve bundle 315 and is connected to lead 320 to applystimulation. Nerve bundle 315 is adjacent vessel 310. FIG. 3Billustrates a transvascular (or intravascularly-fed) electrode for usewith a system for providing stimulation current, according to oneembodiment. The transvascular electrode 304 is placed within a vessel310, is connected to a lead 320, and applies stimulation to an adjacentnerve bundle 315. Other electrode designs may be used without departingfrom the scope of this disclosure. The disclosed system and methods canbe used with devices providing other types of electrical stimulation,including but not limited to pacing, defibrillation, and cardiac rhythmmanagement therapy.

Implantable Medical Devices

FIG. 4 illustrates a block diagram of a system with an IMD for providingstimulation current, according to one embodiment. The system includes animplantable medical device (IMD) 401, an electrical lead 420 coupled tothe IMD 401, and at least one electrode 425. The IMD includes acontroller circuit 405, a memory circuit 410, a telemetry circuit 415,and a neural stimulation circuit 435. The controller circuit 405 isoperable on instructions stored in the memory circuit to deliver anelectrical neural stimulation therapy. Therapy is delivered by theneural stimulation circuit 435 through the lead 420 and the electrode(s)425. According to various embodiments, the neural stimulation circuit435 includes a power supply, circuitry adapted to detect a parameterdependent on tissue/electrode impedance and further adapted to beconnected to the power supply, a current output pulse generator adaptedto deliver electrical therapy, the generator including an adjustablecompliance voltage source connected to the power supply, the compliancevoltage source having a programmable amplitude and adapted to providedifferent potentials for different tissue/electrode interfaceimpedances, as described above in FIG. 1. The telemetry circuit 415allows communication with an external programmer 430. The programmer 430can be used to adjust the programmed therapy provided by the IMD 401,and the IMD can report device data (such as battery and lead resistance)and therapy data (such as sense and stimulation data) to the programmerusing radio telemetry, for example. According to various embodiments,the IMD 401 applies electrical stimulation therapy using a currentoutput pulse generator having an adjustable compliance voltage, detectstissue/electrode interface impedance, and adjusts the level of thevoltage source based on the measured value of tissue/electrode interfaceimpedance, as disclosed in the method depicted in FIG. 8, describedbelow. The illustrated system also includes sensor circuitry 440 that iscoupled to at least one sensor 445. The controller circuit 405 processessensor data from the sensor circuitry and delivers a therapy responsiveto the sensor data.

The electrical lead 420 includes a direct stimulation lead for providingstimulation directly to a nerve trunk, according to one embodiment. Anexample of a direct stimulation lead includes a lead with a nerve cuff,as depicted in FIG. 3A. In an embodiment, the at least one neuralstimulation lead 420 includes an indirect stimulation lead for providingstimulation indirectly to a nerve trunk, through the wall of an adjacentblood vessel. Examples of indirect stimulation leads include chronicallyimplanted transvascular neural stimulation leads, as depicted in FIG.3B. According to various embodiments, the disclosed systems and methodscan be used with a leadless device. For example, in an embodiment, oneor more satellite electrodes are controlled wirelessly to deliverelectrical therapy.

FIG. 5 illustrates a programmer 522, such as the programmer 430illustrated in the system of FIG. 4 or other external device tocommunicate with the implantable medical device(s), according to oneembodiment. An example of another external device includes PersonalDigital Assistants (PDAs) or personal laptop and desktop computers in anAdvanced Patient Management (APM) system. The illustrated device 522includes controller circuitry 545 and a memory 546. The controllercircuitry 545 is capable of being implemented using hardware, software,and combinations of hardware and software. For example, according tovarious embodiments, the controller circuitry 545 includes a processorto perform instructions embedded in the memory 546 to perform a numberof functions, including communicating data and/or programminginstructions to the implantable devices. The illustrated device 522further includes a transceiver 547 and associated circuitry for use tocommunicate with an implantable device. Various embodiments havewireless communication capabilities. For example, various embodiments ofthe transceiver 547 and associated circuitry include a telemetry coilfor use to wirelessly communicate with an implantable device. Theillustrated device 522 further includes a display 548, input/output(I/O) devices 549 such as a keyboard or mouse/pointer, and acommunications interface 550 for use to communicate with other devices,such as over a communication network.

FIG. 6 is illustrates block diagram illustrating an embodiment of anexternal system to communicate with the IMD(s), according to oneembodiment. The external system 1285 includes a programmer, in someembodiments. In the embodiment illustrated in FIG. 6, the externalsystem includes a patient management system. As illustrated, externalsystem 1285 is a patient management system including an external device1286, a telecommunication network 1287, and a remote device 1288.External device 1286 is placed within the vicinity of an IMD andincludes external telemetry system 1289 to communicate with the IMD.Remote device(s) 1288 is in one or more remote locations andcommunicates with external device 1286 through network 1287, thusallowing a physician or other caregiver to monitor and treat a patientfrom a distant location and/or allowing access to various treatmentresources from the one or more remote locations. The illustrated remotedevice 1288 includes a user interface 1290.

Methods for Making a System for Providing Stimulation

FIG. 7 illustrates a flow diagram of a method for making a system forproviding stimulation current from an IMD, according to one embodiment.An embodiment of the method 700 includes forming circuitry adapted todetect a parameter dependent on tissue/electrode impedance, at 702. Themethod embodiment also includes forming a current output pulse generatoradapted to deliver electrical therapy, the generator including acompliance voltage source having a programmable amplitude and adapted toprovide different potentials for different tissue/electrode interfaceimpedances, at 704.

According to various embodiments, forming a current output pulsegenerator includes forming the voltage source to be adjusted using anelectronic feedback loop to maintain a fixed voltage differentialbetween the compliance voltage and a load voltage. Forming a currentoutput pulse generator includes the forming the voltage source to beadjusted using a look-up table that includes a measured tissue/electrodeinterface impedance and a desired level of stimulation current,according to various embodiments. Forming a current output pulsegenerator includes the forming the voltage source to be adjusted usingan external device, in an embodiment. The external device, such as aprogrammer (FIG. 5) or patient management system (FIG. 6) adjusts thevoltage source using a measured tissue/electrode interface impedance anda desired level of stimulation current, in various embodiments.

Methods for Providing Stimulation Current

FIG. 8 illustrates a flow diagram of a method for providing stimulationcurrent from an implantable medical device, according to one embodiment.An embodiment of the method 800 includes applying electrical stimulationtherapy using a current output pulse generator having an adjustablecompliance voltage source, at 805. The method embodiment also includesdetecting a parameter dependent on tissue/electrode interface impedance,at 810. The method embodiment further includes adjusting the level ofthe voltage source based on the detected parameter, at 815. According tovarious embodiments, applying electrical stimulation therapy includesapplying neural stimulation therapy, such as vagal stimulation therapy.The method further includes adjusting the voltage source based on aprogrammed amplitude of the current pulse generator, according to anembodiment.

One of ordinary skill in the art will understand that, the modules andother circuitry shown and described herein can be implemented usingsoftware, hardware, and combinations of software and hardware. As such,the illustrated modules and circuitry are intended to encompass softwareimplementations, hardware implementations, and software and hardwareimplementations.

This application is intended to cover adaptations or variations of thepresent subject matter. It is to be understood that the abovedescription is intended to be illustrative, and not restrictive. Thescope of the present subject matter should be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

1. An apparatus for delivering electrical neural stimulation therapy toa patient, the apparatus comprising: a power supply terminal adapted tobe connected to a power supply; circuitry connected to the power supplyterminal and adapted to detect tissue/electrode interface impedances;and a current output pulse generator comprising a programmed amplitudeof stimulation current, wherein the generator is adapted to deliverelectrical neural stimulation therapy at the programmed amplitude, thegenerator further comprising: an adjustable compliance voltage sourceconnected to the power supply terminal, the voltage source comprising anadjustable voltage level and is adapted to provide different potentialsfor different tissue/electrode interface impedances; and a controlleradapted to receive the detected impedances, maintain the programmedamplitude of stimulation current for the different tissue/electrodeinterface impedances and adjust the compliance voltage source byadjusting the voltage level based on the programmed amplitude of thestimulation current and the detected impedances.
 2. The apparatus ofclaim 1, further comprising an electronic feedback loop, wherein theapparatus is configured to adjust the voltage source using theelectronic feedback loop to maintain a fixed voltage differentialbetween the compliance voltage level and a load voltage.
 3. Theapparatus of claim 1, further comprising storage with a look-up tablestored therein, wherein the look-up table includes tissue/electrodeinterface impedance and desired level of stimulation current, whereinthe apparatus is configured to adjust the voltage source using thelook-up table.
 4. The apparatus of claim 1, wherein the apparatus isconfigured to communicate with an external device to adjust thecompliance voltage source.
 5. The apparatus of claim 4, wherein theexternal device is part of an advanced patient management system (APM).6. The apparatus of claim 1, wherein the apparatus is fully implantable.7. The apparatus of claim 1, wherein the apparatus is partiallyimplantable, and the current output pulse generator of the apparatus isimplantable.
 8. The apparatus of claim 1, further comprising anenclosure configured to house the power supply, the current output pulsegenerator, the adjustable compliance voltage source and the circuitry.9. An apparatus for delivering electrical neural stimulation therapy toa patient, the apparatus comprising: a power supply; circuitry connectedto the power supply and adapted to detect tissue/electrode interfaceimpedances; and a current output pulse generator comprising a programmedamplitude of stimulation current, wherein the generator is configured todeliver electrical neural stimulation therapy at the programmedamplitude, the generator further comprising: an adjustable compliancevoltage source connected to the power supply, the voltage sourceconfigured to provide different potentials for the differenttissue/electrode interface impedances and comprises: an adjustablevoltage level; a supply capacitor; two variable current sourcesconnected in parallel with the supply capacitor; and switches configuredto control the delivery of electrical neural stimulation therapy,wherein the switches are connected to the current sources and supplycapacitor, wherein the pulse generator is configured to receive thedetected impedances, maintain the programmed amplitude of stimulationcurrent for the different tissue/electrode interface impedances andadjust the compliance voltage source by adjusting the voltage levelbased on the programmed amplitude of the stimulation current and thedetected impedances.
 10. The apparatus of claim 9, wherein the voltagesource is adjustable over a range from 1V to 100V.
 11. The apparatus ofclaim 9, wherein the circuitry is configured to detect tissue/electrodeinterface impedances in a range of impedance values from 100Ω to 2 kΩ.12. The apparatus of claim 9, wherein the current output pulse generatoris configured to deliver electrical current over a range from 5 μA to 10mA.
 13. The apparatus of claim 9, further comprising: at least onestimulating electrode, wherein the current output pulse generator isconfigured to deliver electrical therapy using the at least oneelectrode.
 14. The apparatus of claim 13, wherein the neural stimulationtherapy includes vagal stimulation therapy.
 15. The apparatus of claim13, wherein the at least one stimulating electrode includes atransvascular electrode.
 16. The apparatus of claim 13, wherein the atleast one stimulating electrode includes nerve cuff electrode.
 17. Theapparatus of claim 9, wherein the apparatus is fully implantable. 18.The apparatus of claim 9, wherein the apparatus is partiallyimplantable, and current output pulse generator of the apparatus isimplantable.
 19. The apparatus of claim 9, further comprising anenclosure configured to house the power supply, the current output pulsegenerator, the adjustable compliance voltage source and the circuitry.20. The apparatus of claim 9, further comprising an enclosure configuredto house the current output pulse generator and the circuitry.